Three phase rotating ring display with multi stator windings

ABSTRACT

A data display device which includes an indicia-carrying rotor driven by three multi-pole stators which extend collectively around the rotor. The rotor caries a plurality of equally spacedapart magnetic domains upon which the three stators act in succession. Some of the stators are individually driven, each by a separate coil. Other stators share a common coil, resulting in a saving in cost, weight, and size. The use of a single permanent magnet to steadily magnetize several stators is also disclosed.

ilriited States Patent [1 1 Sept. 18, 1973 THREE PI-IASE ROTATING RING DISPLAY WITH MULTI-STATOR WINDINGS [76] Inventor: Hans G. Dill, 2870 Tobago Pl., Costa Mesa, Calif.

22 Filed: Jan. 26, 1972 211 Appl.No.:220,930

[52] US. Cl. 340/378 R, 340/379 R ['51] Int. Ch... G08b 5/00 [58] Field of Search 340/378, 379 R [56] References Cited UNITED STATES PATENTS 3,098,221 7/1963 Propster 340/378 MW y puns Primary Examiner-Harold l. Pitts Attorney-Joseph E. Szabo [57] ABSTRACT A data display device which includes an indiciacarrying rotor driven by three multi-pole stators which extend collectively around the rotor. The rotor caries a plurality of equally spaced-apart magnetic domains upon which the three stators act in succession. Some of the stators are individually driven, each by a separate coil. Other stators share a common coil, resulting in a saving in cost, weight, and size. The use of a single permanent magnet to steadily magneti ze several stators is also disclosed.

12 Claims, 21 Drawing Figures Pmimmserw a 3.760.410 SHEET 30F 7 PATENTEU sm 8 ma saw u or 7 fJf-f-j Q PATENTEDSEPI ems SHEET 7 BF 7 THREE PHASE ROTATING RING DISPLAY WITH I MULTI-STATOR WINDINGS BACKGROUND OF THE INVENTION .There exists a need in many areas of technology to display digitally signalled data accurately, inexpensively, and reliably. One such area is in the field of timekeeping devices, and in particular, in electronic watches working on digital principles. A display device particularly designed for electronic watch applications, but also useful for displaying other types of data, is disclosed in patent application Ser. No. 146,199, filed by Hans G. Dill on May 24, 1971, and entitled, Rotating Ring Display. The rotating ring display described in the referenced patent application includes a rotating ring, or rotor, carrying indicia which are to be displayed. The rotor is advanced in equal steps by an arrangement which includes a plurality of magnetic domains on the rotor and a plurality of driving means in the form of two or three magnetic stators distributed around the periphery of the rotor. Each stator includes a permanent magnet, with magnets being so distributed around the periphery of the ring as to hold it stably in a plurality of equally spaced rest positions. The stators also include electric coils wound thereon and energized in succession so as to modify the effect exerted by the magnets upon the magnetic domains, thereby causing a net thrust to beexerted on the rotor, driving it from a given one of its rest positions to the next such position. A particularly advantageous feature of the above arrangement is that no power is required to maintain the rotor in its rest positions, since this is achieved by the permanent magnet.

An improved information display device working on the above-described rotating ring principle is disclosed and claimed in a second patent application, Ser. No. 174,695, filed by Hans G. Dill on Aug. 25, 1971, and entitled, Three Phase Rotating Ring Display."

In the improved display device an indicia-carrying rotor, carrying a plurality of spaced-apart magnetic domains (or areas) is surrounded by three multi-pole stators. Preferably, the magnetic domains are evenly distributed around the rotor and each stator has a plurality of arcuately distributed gaps through which the domains pass as the rotor turns and which become aligned with respective magnetic domains of the rotor at the same time. The gaps of all three stators do not become aligned with the rotor domains at the same time, however. Rather, they are so distributed about the periphery of the rotor that, as the rotor moves through successive rest positions, its domains become successively aligned with the gaps of respective ones of the three stators. Means are provided to maintain a magnetic field across the gaps of all three stators so that, as the rotor reaches successive ones of its rest positions, it is firmly held in those positions by the magnetic field of the particular stator with which its magnetic domains are aligned. One of the advantages of the improved display device is that the rotor is held very firmly in its rest positions, this being the result of the simultaneous alignment of a plurality of its domains with a corresponding plurality of stator gaps. Preferably, the means for maintaining a magnetic field across the stator gaps includes a permanent magnet, so that no power-need be consumed while the rotor is in one of its rest positions.

To advance the rotor from a given one of its rest posi tions to the next such position, means are provided to modulate the magnetization of the stators in cyclic succession. More specifically, in accordance with a preferred embodiment of the improved display device, each stator is provided with a coil which is so coupled to the stator that when the coil is energized, the magnetic field exerted by the permanent magnet across the stator gap is diminished and, preferably, neutralized. Moreover, the stators are so arranged that, when the gaps of one are aligned with the rotor domains, the other twostators are out of alignment with the rotor domains by equal but opposite amounts. As a result, with none of the stator coils energized, the aligned stator tends to hold the rotor in its rest position while the two non-aligned stators exert equal but opposite forces upon the rotor. Consequently, the rotor may be advanced from its rest position to the next such position by energizing the coil of one of the two non-aligned rotors so as to unbalance their opposed forces. Which of the two non-aligned stators is energized depends on the desired direction of rotation. Also, preferably the coil of the aligned stator is also energized so as to release its hold upon the rotor during the period when the rotor is to be advanced.

Where several display rotors are used in a single display device, and particularly where size, weight, and cost are important factors, the number of coils may become excessive if one of them is used for each stator, or three coils for each rotor.

It is the principal object of the present invention to reduce the number of coils required for a multi-rotor rotating ring display device to less than the number of rotors times the number of stators per rotor.

More specifically, it is the object of the present invention to perform with common coils the functions which were previously performed by several of them. It is a related object of the present invention to reduce the number of permanent magnets required by using only one such magnet for the stator of a given phase for all rotors, rather than using one magnet for each such stator.

The present invention finds its greatest utility when applied to a display device which includes a plurality of indicia-carrying rotors, each having a plurality of magnetic domains, and a first, a second, and a third multipole stator associated with and magnetically coupled to the domains of each of the plurality of rotors.

In accordance with the present invention, common means are provided for periodically alteringthe magnetization of all of the first stators (referred to herein as phase II) together in response to a first series of electric pulses. As disclosed herein,the common means may include a single electric coil which is coupled magnetically to all of the first stators. In further keeping with the invention, means are provided for steadily magnetizing each of the second stators (referred to herein as phase I), and this means may include a single perma- 4 nent magnet magnetically coupled to all of the second stators. Lastly, individual means are provided for periodically altering the magnetization of at least one of the third stators (referred to herein as phase III) associated tion of the first stators of all rotors are altered in unison, and even though the second stators of all of the rotors may also be steadily magnetized by a single magnet. Thus, one coil and, if desired, one magnet, may serve a given set of stators of all of the rotors of the display device rather than requiring a separate coil and a separate magnet for each of those stators.

The display device of the present invention may take two specific forms. In accordance with the first specific form of the invention, the individual means for periodically altering the magnetization of one or the other of the second and third stators of each rotor includes a .separate coil coupled magnetically to each of the second stators only. The third stators are provided with a second common means (such as that associated with the first stators) for periodically altering their magnetizations together in response to a third series of electric pulses whose phase is different from that of both the first series of pulses driving the first stators and the additional series of pulses driving the second stators.

The embodiment of the invention just described may be characterized as having a three-phase drive, two of whose phases are associated with the first and third stators of the rotors and whose remaining phase serves individually to alter the steady magnetizations of the second stators associated with the respective rotors. Assuming that each of the common means includes a single coil, which is the most desirable embodiment of the invention, the last described, three-phase embodiment of the present invention is characterized by having N 2 coils, where N is the number of rotors of the device.

In accordance with another specific embodiment of the present invention, the individual means for periodically altering the magnetization of one or both of the second and third stators of each rotor includes a separate coil coupled magnetically to each of the third stators only. The latter embodiment of the invention may be characterized as having a two-phase drive, one of whose phases is the common drive for the first stators of all of the rotors and whose other phase is the individual drive for respective ones of the third stators of the rotors. In contrast to the first described specific embodiment, the steady magnetization of the second stators of the various rotors is not altered here. The second specific embodiment of the present invention is characterized by N l coils, where N is defined as above.

From the foregoing brief description, it is apparent I that the configuration of the display device of the present invention is effective to substantially reduce the number of coils from 3N to N l, or N 2. Thus, the reduction, in the case of a five rotor display device, is from to 6 or 7, or better than half. Moreover, since the present invention also permits a single magnet to serve a given set of stators associated with all of the rotors, a significant reduction in the number of magnets required is also made possible.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in greater detail by reference to the following drawings, in which:

FIG. 1 illustrates an one possible application of the present invention a multi-ring display device, with the rings being illustrated with various types of exemplary indicia;

FIG. 2 is a schematic diagram of the previously described earlier improved display device whose three multiple stators each extend approximately one-third around the periphery of its rotor, each stator having its own coil and permanent magnet;

FIG. 3 is a sequential pulse timing diagram schematically showing the ring of FIG. 2 in four successive positions and the corresponding energization ofits three stators;

FIG. 4 is a perspective view illustrating schematically one possible configuration which the display device of FIG. 2 may take;

FIG. 5 is a diagram similar to FIG. 4 and showing an alternative configuration for the display device of FIG.

FIG. 6 is a sectional view illustrating in more detail the manner in which the FIG. 4 embodiment of the FIG. 2 device may be constructed;

FIGS. 8c illustrate three exemplary configura tions of the rotor shown schematically in FIG. 2;

FIG. 9 is a schematic diagram of one embodiment of the present invention wherein a plurality of rotors have two of their three stators driven by common coils and wherein the steady magnetization of the third stator of each rotor is individually altered periodically.

FIG. 10 is a cross-section through a display device to illustrate the manner in which a single coil is magnetically coupled to the stators of three rotors.

FIG. 1 l is a plan view of the single coil and associated flux paths and stators illustrated in FIG. 10, but with the plastic body in which those elements are embedded being omitted for clarity.

FIG. 11a is a perspective view of the elements shown in plan view in FIG. 11.

FIG. 12 is a sequential pulse timing diagram schematically showing one of the rotors of FIG. 9 in four successive positions and the corresponding energization of its three stators.

FIG. 13 is an additional pulse timing diagram to show the relative durations of the electric pulses driving the three stators of the FIG. 9 device.

FIG. 14 is a schematic diagram of the second principal embodiment of the present invention in which the several rotors of the display device are driven by a single common coil and by an additional coil coupled individually to a stator of each of the rotors, there being no coils associated with the third set of stators which are steadily magnetized, preferably with one or more permanent magnets.

. FIG. 15 is a sequential pulse timing diagram schematically showing one of the rotors of FIG. 14 in four successive positions and the corresponding energization of two of its three stators.

FIG. 16 is an additional pulse timing diagram, similar to FIG. 13, to show the time durations of the electric pulses used to drive the stators of FIG. 14.

FIG. 17 is a schematic diagram to illustrate the permanent magnet and associated flux paths used to steadily magnetize one of the stators of either the FIG. 9 or FIG. 14 display device and also to show the electric coils for individually altering the steady magnetization of the stators of the FIG. 9 device.

FIG. 18 is a plan view, partially broken away, of one possible physical configuration which the arrangement of FIG. 17 may take.

DESCRIPTION OF THE PREFERRED EMBODIMENT While the invention has been shown and will be described in some detail with refcrcnce to preferred cmbodimcnts thereof, there is no intention that it must be limited to such detail. On the contrary, it is intended here to cover all modifications, alternatives,-and equivalents falling within the spirit and scope of the invention as defined by the appended claims.

Turning now to the figures, an exemplary application of the present invention is the multi-ring display 11 illustrated in FIG. 1. As shown in FIG. 1, the earlier exempla'ry display 11 may include a casing 13 supporting a dial 15, below which a plurality of rings 17, 19, and 21 are rotatably supported in a concentric relationship. Preferably, although not necessarily, each of the rings is separately sealed in the casing 13, being held in individual concentric grooves. Each of the rings is marked with indicia which may take the form of a moving circular band 22, or a pointer 24, both of them being read against a stationary scale on the dial, or it may take the form of a number, 23, which is displayed through a transparent window 25 in an otherwise opaque lens. Naturally, any combination of such indicia may be employed, as illustrated in FIG. 1.

The present invention is directed primarily to the manner of driving each of the respective rings 17, 19, and 21. There will first be described in some detail, with reference to FIGS. 1-8, the aforementioned threephase rotating ring display device disclosed and claimed in the second referenced Dill application, Ser. No. l74,695, wherein each stator is shown to have a separate coiland magnet. Subsequently, there will be described, with reference to FIGS. 9-18, the modifications whereby the FIG. 2 device may be changed in accordance with the present invention to operate with a significantly smaller number of coils and magnets.

For sake of simplicity, a display device 27, illustrated schematically in FIG. 2, is shown as having only a single ring. The device 27 is comprised principally of a rotor or ring 29 carrying a plurality of magnetic domains 31 which are preferably evenly distributed. Since the nature of the rotor 29 will be discussed in greater detail, it is sufficient, at this point, to understand that the magnetic domains 31 are regions on the rotor 29 which provide a better flux path than other areas of the rotor.

It should be clearly understood that the phrase, magnetic domain, is not being used herein to describe a unidirectionally saturated ferromagnetic crystal, a meaning which that phrase has acquired in theoretical physics.

Extending along the periphery of the rotor 29 are three stators 33a, 33b, and 33c, each of which runs approximately one-third around the periphery of the ring. Generally, the stators 33a-33c are actuated with three different phases of driving current and serve successively to advance the rotor 29 from a given one of its rest positions to the next such position. In the exemplary embodiment illustrated in FIG. 2, each of the stators 33a-33c includes a first pole piece 35 and a second omctry used to crcatc the space and the field. In order to cause such a magnetic field to appear simultaneously across the several gaps 39 of a given stator, each such stator is provided with means 45 for magnetizing it. Such means is shown to include a permanent magnet 47 and a magnetic member 49 for applying the magnetic field of the magnet across the pole pieces 35 and 37 of the stator. Means are also provided for modulat' ing the magnetic field applied by the magnet 47 across the gaps 39, this being shown in the form of'a coil 51 wound around the magnetic member 49 which is connected at one of its ends to the stator pole piece 35 and at its opposite end to the stator pole piece 37.

To advance the rotor 29, a current pulse is applied to the respective coils 51 marked, respectively, I, II, and III, from a three-phase pulse train generator 53. The details of such a generator need not be described, since anyone skilled in the art of electronics will be able to construct-one, given the necessary phase relationships of the pulse trains which are to be applied to the respective coils 51. These phase relationships are shown in FIG. 3, in which the position of the rotor 29 is shown at four successive times, t t and t.,. The successive positions of the ring are shown in relation to the position of the stator pole fingers 41, of which one is shown for each of the three stators 33a, 33b, and 330, and which are respectively identified by the phaserepresentative symbol 1, II, and III.

Before proceeding further, it will be helpful in understanding the following discussion to observe the positions of the respective stators 33a-33c relative to the rotor 29. Thus, it will be noted that the phase I stator 33a has its pole teeth 41 and 43 in alignment with the rotor domains 31, which extend between them. At the same time, the phase II and phase III stators 33b and 330 are out of alignment with the magnetic domains which extend between respective ones of them by equal and opposite amounts. In particular, the phase II stator 33b has its poles 41, 43 ahead of the magnetic domains 31 which lie between them, and this lead is twothirds of the peripheral extent of one of the magnetic domains. Conversely, the phase III stator 330 has its poles 41, 43 lagging the magnetic domains 31 lying be-- tween them, by two-thirds of the peripheral extent of a domain. The above lag and lead figures assume a clockwise advancement of the rotor 29. Accordingly, when none of the stator coils 51 is energized, the phase I stator 33a will securely hold the ring 29, due to the fact that its domains 31 are aligned with the poles 41, 43 of the stator. Moreover, the permanent magnetic fields which exist between the poles of the phase II and phase III stators 33b and 330, will exert equal but opposite rotational forces upon the ring 29, so that the rotor remains stationary. All that is necessary, then, to advance the rotor 29 is to unbalance the forces which are exerted upon it by the phase II and phase III stators 33b and 330. While not essential, it is desirable also, at the same time, to diminish and preferably eliminate the holding effect of the phase I stator 33a, in order to permit the rotor to move more easily.

To advance the rotor 29 from the rest position in which it is illustrated in FIG. 2 to its next rest position, all that is necessary is to apply a current pulse to the coils 51 of the phase I and phase III stators, the pulses being in a direction such that the magnetic field of the respective permanent magnet 47 across the gaps of those stators is diminished. This will result in a clockwisc advancement of the rotor 29, since the force exerted by the phase II stator 33h, ending to move the rotor clockwise, will be greater than the corresponding force exerted by the phase III stator 33(', whose effect would normally be to urge the ring 29 counterclockwise. This state of affairs is illustrated in FIG. 3 as occurring at time t where a magnetic domain 31 is shown to be in alignment with the pole tooth 41 of the phase I stator and where a pulse is shown to be applied to the phase I and phase III coils, but not to the phase II coil, this being indicated by the numeral (1) next to the phase l and phase III pole teeth 41 and by the numeral next to the phase II pole 41.

The position reached by the ring 29 after the application of the aforementioned current pulses is shown at time I, in FIG. 3 to be such that the pole teeth 41 of the phase II stator are in alignment with the rotor domains 31. Accordingly, the next combination of pulses is such that the coils 51 associated with the phase I and phase II stators 33a and 33b are energized. Hence, by the same reasoning advanced hereinabove with reference to the previous position of the ring 29, it is rotated through an angle corresponding to two-thirds of the angle occupied by a domain 31 under the attractive force of the phase III stator 33c. This brings the rotor 29 to the position shown for time t,, where its magnetic domains are aligned with the pole teeth 41 of the phase II stator 33b. Therefore by the above reasoning, current pulses are applied to the phase I and phase II stators 33a and 33b, causing the rotor 29 again to be stepped through two-thirds of the angle occupied by one of the magnetic domains 31, causing it to reach the position shown in FIG. 3 to exist at time t,, from which it migh be advanced to its next rest position by the application of current pulses to the phase II and phase III stators.

The provision of a plurality of poles 41,43 for each stator is advantageous, in that it improves both the holding power of the stator for a given strength permanent magnet, and also increases the torque exerted by the stator upon the rotor, as compared to what it would be, had the stator only a single pole. Additionally, since there are several magnetic domains interacting at the same time with a given stator, performance of the display device is not seriously affected if, at a given time, fewer than all of the poles of the stator interact with magnetic domains on the rotor. Consequently, it becomes permissible to omit or otherwise alter the characteristics of one of the rotor domains so as to provide a magnetically or electrostatically detectable reference point thereon. Accordingly, in accordance with a feature of the invention as shown in FIG. 2, in the area 55 midway between the magnetic domains 31a and 31b where an additional magnetic domain would normally be located, the rotor is left devoid of such a domain, or, in other words, the magnetic domain is omitted. To permit detection of the reference point thus provided on the rotor, a magnetic pick-ofi 57 is provided. It includes a pair of poles 58 on opposite sides of the rotor, a magnetic member 59 connecting the poles 58, and a sensing coil 60, wound on the member 59. In each of the rest positions of the rotor 29, the magnetic reluctance of the flux path constituting the magnetic member 59 and its poles 58 will be at a given level which will be relatively low, due to the coupling provided by the magnetic domains 31 disposed between the pick-off poles 58. In a single rest position of the rotor, however; namely, when the domain-free area 55 of the rotor is between the pick-off poles 58, the magnetic reluctance of the pick-off flux path coupled to the sensing coil 60 will be at a higher level due to the lack of coupling between the pick-off poles 58. By means well known to those skilled in the art, the difference can be detected by the sensing coil 60. Such a device is represented by the zero reset control circuit 62, whose output is shown to be applied to the three-phase pulse train generator 53. The circuit 62 may additionally include an automatic reset feature whereby the three-phase pulse train generator 53 is directed to energize the stators 33a-33c, so long as a magnetic domain 31 is sensed by the pick-off 57 and to terminate such pulses when the missing" domain 55 reaches the pick-off device. It will be understood, of course, that the reference region 55 may differ from the magnetic domain regions of the rotor in other characteristics, such as conductivity. For example, in addition to omitting a magnetic domain, the area which it would normally occupy on the rotor may be made conductive so as to permit it to be sensed by capacitive sensing means.

Turning now to FIGS. 4 and 6, one preferred embodiment of the display device operating along the principles discussed with reference to FIG. 2 features a substantially flat ring-shaped rotor 65 whose principal plane is at right angles to its axis of rotation, and on which a plurality of magnetic domains 66 are disposed in equally spaced-apart relation, with each domain occupying a segment of the rotor which is equal in size to the segment between adjacent domains. Extending along one face of the rotor 65 is an upper pole piece 61 of magnetic material such as soft" iron, having a plurality of radially inwardly extending teeth 67, joined by an arcuately extending connecting rib 69. The respective teeth 67 are substantially coextensive with the corresponding magnetic domains 66. Extending along the opposite side of the ring 65 is a lower pole piece 63 of the same material as the upper pole piece and having a plurality of radially outwardly spreading teeth 71 joined by a connecting rib 73 and substantially coextensive with the upper set of teeth 67. Thus, respective pairs of teeth 67 and 71 define a plurality of arcuately extending poles having gaps between them through which the magnetic domains 66 move as the rotor 65 turns. A magnetic field is maintained across each of these gaps by a permanent magnet 75 which is connected by means of a magnetic cross piece 77 to a downwardly extending portion 73a of the lower pole piece connecting member 73 and which is connected to the upper pole piece 61 through a downwardly extending member 69a of its connecting rib 69. Wound around the cross piece 77 is a coil 78 to which current may be applied to modulate the magnetic field imposed across the gaps between the pole pieces 61 and 63 by the permanent magnet 75.

As best seen in FIG. 6, the entire assembly is housed in a plastic pill-shaped easing which includes a plastic body 81, a back 83, and a top 79. For convenience of assembly, the upper and lower pole pieces 61 and 63 are respectively anchored in the top 79 and the body 81 by casting them in place. In this manner, cross members 82 are formed in and of the casing body 81, for supporting the teeth 71 of the lower pole piece 63. The coil 78, the cross piece 77, and the magnet 75 are then placed in their positions within an opening 85 provided for them in the casing body.

With the lower pole piece 63, the coil 78, the cross piece 77, and the magnet 75 in place in the casing body 81, the rotor 65 is placed in position on top of the teeth 71 inside the casing recess 85, after which the casing top 79 carrying the upper pole piece 61 is inserted into the casing body 81. For this purpose, the top 79 is provided with a downwardly extending supporting rib 89 which serves both to lock the top in place in the body 81 and also to support the extension 69a of the upper pole piece 61. Finally, the casing bottom 83 is pushed into place so as to seal the assembly. It will be understood that the remaining two sets of upper and lower pole pieces are distributed in themanner shown schematically in FIG. 2, each occupying approximately 120 of are. It will also be apparent that several display devices such as the one illustrated in FIGS. and 6 may be housed in a common casing concentrically, in the manner illustrated schematically in FIG. 1.

A second exemplary embodiment of a display device,

operating on the principles illustrated schematically in FIG. 2 is shown in FIGS. 5 and 7. It differs from the embodiment of FIGS. 4'and 6 primarily in that its rotor 91 is T-shaped in cross-section, with the central leg 93 of the rotor extending parallel to its axis of rotation. Each of the three stators of the device, of which only one is illustrated in FIG. 5, includes an inner pole piece 95 which extends along the inside of the rotor 91 and an outer pole piece 97 which extends along the outside of the rotor. The inner pole piece 95 has an arcuately extending connecting member 99 from which a plurality of spaced-apart teeth 101 extend axially, parallel to the body of the rotor 91. Similarly, the outer pole piece 97 is comprised of 'a connecting member (not shown) from which a plurality of teeth 103 extend, there being one tooth 103 opposite each of the .teeth 101 of the inner pole piece 95, each pair of opposed teeth defining a stator pole 101, 103. Magnetic domains 105 are distributed at equal intervals along the body of the rotor 91, with the length of a given domain corresponding with that of the teeth 101 and 103 and with the spacing betweenadjacent domains similarly corresponding to the spacing between adjacent ones of the poles 101, 103. For a more convenient display of indicia, the central rotor member 93 is provided with a flat, preferably non-magnetic, cross piece 107.

To establish a magnetic field across the gaps between the respective poles 101, 103, a permanent magnet 109 is placed in a magnetic circuit across the pole pieces 95 and 97 by means of a magnetic cross member 111,

around which a coil 113 is wound for modulating the magnetic field across the respective gaps of this stator.

Thus, the rotor 93 provides an example of a display device in which the rotor does not have indicia directly marked on it but instead carries a non-magnetic ring on which the indicia are marked. It should be understood,

therefore, that when the phrase, indicia-carrying rotor is used herein, it is meant to include a rotor carrying indicia, either directly as in FIG. 4, or indirectly on another ring, as in FIG. 5.

To establish a magnetic field across the gaps between the respective poles 101, 103, a permanent magnet 109 is placed in a magnetic circuit across the pole pieces 95 and 97 by means of a magnetic cross member 111, around which a coil 113 is wound for modulating the magnetic field across the respective gaps of this stator.

With the pole pieces case in place, the magnet 109, the cross piece 111, and the coil 113 are placed in position and secured in an opening 121 provided for them in the body 115, after which the bottom 119 is pressed in place. The rotor 91 is then seated between the teeth of the inner and outer pole pieces and 97, after which the casing top 117 is secured in the body 115. For this purpose, the casing body is provided with a pair of annular grooves 127 and the casing top 117 is provided with a pair of annular tongues 129, which fit snugly into the grooves 127, creating a sealed chamber 131 for the rotor 91. It will be noted that a similar sealed chamber is also provided by the arrangement shown in FIG. 6 for its rotor 65.

The rotor 29 of the display device illustrated in the foregoing figures may take several alternative forms, three of which are illustrated in FIGS. 8a, 8b, and 80. For the sake of reference, each of the three stators 31a, 31b, 310 of FIG. 2 is represented by one of its poles 41, 43, located in their proper positions next to the rotor and identified by the phase labels 1, II, III.

The rotor illustrated in FIG. 8a in cross section in homogeneously constituted of a magnetic material which may be a magnetic plastic and which has raised or thickened portions 135 serving as the magnetic domains. Thus, it will be seen that the magnetic coupling afforded between the phase I poles 41 and 43 by the thickened rotor portion 135 is much greater than would be the case if the relatively thin portion 137 between adjacent magnetic domains 135 were between those poles. Thus, the effect is the same as if the rotor were of uniform cross section and had intermittent seg ments of its body made of a magnetic material and the remainder of its body made of a non-magnetic material.

The same principle used for the ring of FIG. 8a is also employed with the rotor illustrated in FIG. 8b and which is shown to be comprised of a pair of corrugated magnetic metal rings 139 and 141, preferably made of sof iron, joined together. to produce intermittently thick and thin rotor portions 143 and 145, with the thick rotor portions serving as the magnetic domains of the rotor.

Yet another possible embodiment for the rotor of the present invention, illustrated in FIG. 8c, is comprised of a single corrugated magnetic metal ring 147 which may be sandwiched for rigidity between a pair of flat plastic (non-magnetic) rings 149 and 151. In the case of the rotor embodiment of FIG. 80, each magnetic domain is seen to comprise a pair of oppositely disposed metal sections, such as the sections 153 and 155, and the transversely extending ring portion 157 which connects them. Three magnetic domains of the ring illustrated in FIG. 8c are respectively labeled A, B, and C. Since the essence of a magnetic domain is that it provides magnetic coupling between opposed teeth 41 and 43 of a given pole, it is seen that, because of the peculiar geometry of the magnetic domains illustrated in FIG. 80, each pair of opposed pole teeth 41 and 43 must be staggered relative to each other along the direction of travel of the ring, so that when one-half of the magnetic domain is proximate one of the pole teeth, the opposite half of the domain is proximate the opposite pole tooth, this being the condition of alignment of the magnetic domain with the pole in which magnetic coupling between the pole and the magnetic domain occurs.

FIG. 9 illustrates application of the present invention to a three-ring display device which is constructed substantially along the principles illustrated in and described with reference to FIG. 2, but with several modifications which will be described next. In the FIG. 9 display device the three concentric rotors 229-1, 229-2, and 229-3, may serve the functions of the second, minute, and hour rings 21, 19, and 17 illustrated in FIG. 1. Each of the rotors carries a plurality of magnetic domains like those shown in FIG. 2 for the rotor 29. Moreover, each rotor of the FIG. 9 device is provided with three multi-pole stators, such as the stators 33a, 33b, and 33c, illustrated in FIG. 2. Thus, for purposes of this discussion with reference to each of the following figures it should be understood that each of the rotors has three multi-pole stators, and that the stator poles of the display devices illustrated 'in FIGS. 9-18 have the same geometrical relationships relative to the rotor domains as do the stator poles of FIG. 2. However, whereas in the FIG. 2 embodiment each of the three stators was provided with a permanent magnet 47, in the FIG. 9 embodiment, in keeping with the present invention, only one of the stators has such a permanent magnet, this being shown in FIG. 9 as the phase I stator for each of the three illustrated rotors, the magnets being numbered respectively 247-1, 247-2, and 247-3.

An additional modification made to the FIG. 2 device, in accordance with the present invention, is that rather than providing a separate coil 51 to alter the magnetization of each of the stators of each rotor, requiring three coils for the stators of each rotor, in the FIG. 9 device a single coil 251-2 is coupled magnetically to the phase II stators of all of the rotors of the device. Similarly, in the FIG. 9 embodiment of the present invention, a common coil 251-3 is coupled to the phase III stators of all of the rotors of the device.

FIGS. 10, 11, and 11a illustrate further a suitable configuration represented by the FIG. 9 schematic diagram, and in particular how a single coil 251-2 is magnetically coupled to each of three phase II stators 3312-1, 3311-2, and 33b-3. As best shown in FIGS. 11 and 11a, the coil 251-2 is wound upon a core 301 of magnetic material from each of whose ends three arms extend. From the front end of the core 30] extend the arms 303, 311, and 315. From the back end of the core extend the arms 307, 313, and 319. The first three arms have upwardly extending fingers 305, 311, and 317, respectively, which connect the arms and the core 301 to the pole pieces 235-3, 235-2, and 235-1 of the three stators 33b-3, 33b-2, and 33b-1. Similarly, the three arms which extend from the rear of the core 301 have upwardly extending fingers 309, 313, and 321, which connect them magnetically to the inner pole pieces 237-3, 237-2, and 237-1 of the same three stators. Thus, when the coil 251-2 is energized, a magnetic field is established across the teeth of all three of the stators 33b-1, 3312-2, and 3312-3, simultaneously.

Another set of arms having the configuration shown in FIG. 110 may serve to apply the magnetomotive force of the phase III coil 351-3 of FIG. 9 to the phase III stators of all of the rotors.

In FIG. 10 the one-coil three-stator configuration is shown embedded in plastic, following the same technique explained previously with reference to FIG. 7. Thus, the entire assembly is seen in place in a plastic body 2115, with the bottom being covered with a cap tors rides freely in circular tracks formed under the lens 2117 in the same manner as explained in detail previously with reference to FIG. 7.

Having explained the construction of the drive electromagnetics for phases II and III of the FIG. 9 device, reference will next be made to the phase I portion thereof. From FIG. 9 it is seen that each of the several stators 33a associated with the respective rotors 229-1, 229-2, 229-3, and not illustrated as such in FIG. 9, is provided with means for steadily magnetizing that stator. The means for steadily magnetizing the stators 33a of the rotors shown in FIG. 9 may be individual permanent magnets 247-1, 247-2, and 247-3, each associated with a respective one of the three stators 33a associated with phase I of the three illustrated rotors. Alternatively, as will be discussed hereinafter with reference to FIG. 18, a single permanent magnet may serve the purpose. If a separate permanent magnet is used for the phase I stator of each rotor, as shown in FIG. 9, the electromagnetic configuration whereby the magnetiefield of each permanent magnet is applied to its associated stator 33c may be the same as that illustrated in FIGS. 5 and 7.

The manner in which any selected rotor may be driven by means of the arrangement shown in FIG. 9 will be readily apparent from an inspection of FIGS. 12 and 13. In FIG. 12 the innermost rotor 229-1 is illustrated in four successive positions, at times 1,, t t and t the last of which is a return to its initial position shown at time t,. For simplicity, the rotor is shown as a flat strip, it being understood that its linear advancement to the left corresponding to counterclockwise ro- 2119 and the top being sealed with a transparent lens 2117, through which each of the rotors 229-1, 229-2, and 229-3 may be viewed. Each of the last-named rotation of the rotor. Also, each of the stators 35a, 35b, and 350 is represented by one of its pole teeth 41, as was the case with FIG. 3. At time t,, the rotor 229-1 is illustrated in one of its stable positions, in which it is held by the permanent magnet 247-1, through the pole teeth of the phase I stator 33a, one of which is shown aligned with one of the several spaced-apart magnetic domains 231 of the ring. To move the rotor 229-1 from its initial position to its next position shown at time 1,, the phase I and Phase III coils 251-1-1 and 251-3 are briefly energized (FIG. 13). Energization of the phase I coil 251-1-1 serves to alter the magnetization imposed upon the phase I stator of the rotor 229-1 by the permanent magnet 247-1 in such a way as to diminish the holding force exerted by the phase I stator upon the rotor. This permits the rotor 229-1 to advance toward the left (counterclockwise) under the influence of the pull exerted upon the domain 231 just to the right of the stator 251-3 by the energization of the phase III coil. It will be understood that none of the other rotors is advanced, although their phase III stators are simi- Iarly energized, because their phase I permanent magnets 247-2 and 247-3 continue to hold them in one position, since the coils which are associated with those magnets have not been energized. Of course, all of the rotors may be advanced at the same time, provided that the compensating coils associated with their permanent magnets have also been energized.

It should be noted that the only stable positions of the rotor 229-1 are those shown in FIG. 12 at times t, and I The intermediate positions illustrated at times t, and t exist only temporarily. They are positions through which the rotor 229-1 moves to advance from one of its stable positions shown at r, to the next one of its stable positions shown at 1,. To advance the rotor from its first intermediate position at t, to its second intermediate position shown att thecoil 251-1 1 remains energized (FIG. 13), but the state of energization of the coils 251-2 and 251-3 are reversed, so that the phase II coil is now energized and the phase III coil is now deenergized. This causes a leftward force (as seen in FIG. 12) to be exerted upon the ring 229-1 by the phase II stator, thus adding a leftward thrust (as seen in FIG. 12) to the already moving ring 229-1 To complete the travel of the rotor 229-1 to its second stable position at the next step, taken at time t;,, is to leave all three of the illustrated coils unenergized. This brings into play the magnetic attraction exerted by the phase I stator 33a, as a result of the permanent magnetic field existing across its teeth 241 by virtue of the permanent magnet 247-1. As a result of this attraction, the rotor 229-1 moves into alignment with the stator 33a to reach its second illustrated stable position, shown at time t,.

A second embodiment of the present invention is illustrated in FIG. 14 schematically. It is a multi-ring display device constructed, as the FIG. 9 device, on the design principles illustrated in FIG. 2 and discussed with referencethereto. In the schematic representation of FIG. 14, the stators 33a, 33b, nd 33c are not shown as such but are merely represented by their respective permanent magnets 247-1, 247-2, and 247-3, and coils 251-2, 251-3, 251-3-2, and 251-3-3.

The principal distinction between the FIG. 9 and the FIG. 14 display devices is that in the FIG. 9 device each stator (33a, 33b, 330) is driven by a separate pulse train so that it can be truly characterized as a three-phase drive. In contrast, only the phase II and phase III stators 33b, 330 of the FIG. 14 device are driven by respective pulse trains. The phase I stators 33a are steadily magnetized by a permanent magnet or its equivalent, but their magnetization is not altered by means of a coil pulsed in the manner in which the phase II and phase III coils are. More specifically, the phase I stators 33a of the FIG. 14 device may each be configured as shown in FIGS. 5 and 7, each of them being provided with its own permanent magnet 247-1, 247-2, and 247-3, respectively, to effect a steady magnetization of the respective stators. Alternatively, as will be explained hereinafter with reference to FIG. 18, a common permanent magnet may serve to magnetize all three of the phase I stators 33a. v

The phase II stators of the FIG. 14 device are illustrated as taking the same form as they have in the FIG. 9 device. Again, the stators themselves are not illustrated in FIG. 14 but are merely represented by the common coil 251-2, which is magnetically coupled to all three of them. The FIG. 11a configuration may again be employed.

The phase III stators 330 of the three rotors 229-1, 229-2, and 229-3, are each magnetized individually by respective coils 251-3-1, 251-3-2, and 251-3-3. The operation of the FIG. 14 device may be understood by referring to FIGS. 15 and 16. Again, these figures illustrate how the rotor 229-1 may be advanced from a given one of its stable positions, shown at the time t,, to its next stable position, shown at time t,. The ring is advanced from its first illustrated stable position by applying a current pulse to the phase III coil 251-3-1 of that ring (FIG. 16). This causes the pole teeth of the phase III stator 330 to exert a magnetic pull upon the magnetic domains represented by the particular domain shown just above and to the right of the pole tooth 241 representing the stator 33c.

At time t when the ring 229-1 has advanced toward the left (as seen in FIG. 15) so as to bring the domain referred to previously into alignment with the pole teeth of the phase III stator 330, the phase III coil 251-31 is deenergized and the phase I coil 251-2 is energized by application of a current pulse thereto (FIG. 16). Therelative geometries of the ring 229-1 and of the pole teeth 241 of the stators 33a, 33b, and 33c is such that when the domains arein alignment with the pole teeth of the phase III stator 330 shown in FIG. 15, the domains which are at that time moving through the 'pole teeth 241 of the other two stators 33a and 33b are out of alignment with those stators by equal amounts and in opposite directions, as shown in FIG. 15 at time t Consequently, the magnetic force exerted by energization of the coil 251-2 will have to exceed the magnetic force being exerted upon the rotor 229-1 by the stator 33a in the opposite direction as a result of its permanent magnet 247-1. Provided this condition is met, the ring 229-1 will, in response to the energization of the phase II coil 251-1, advance toward the left into the position in which it is illustrated in FIG. 15 at time wherein the rotor domains 231 are aligned with the pole teeth 41 of the phase II stator 33b and the domains which are within the phase I and phase III stators 33a and 33c are, respectively, lagging and leading their associated stator teeth by equal amounts.

To advance the rotor 229-1 from its position to its second stable position shown at time both of the phase II and phase III coils 251-2 and 251-3-1 are left unenergized (FIG. 16). As a result, the magnetic pull exerted by the phase I stator 33a associated with the rotor 229-1 is unopposed and is effective to complete the advancement of the ring from its position shown at time 1 to the position shown at time t,, at which time its magnetic domains 231 are aligned with the pole teeth 241 of the phase I stator 33a.

A suitable configuration for utilizing a single permanent magnet 247 to steadily magnetize the phase I stators 33a-1, 33a-2, and a33c-3 of the rotors 229-1, 229-2, and 229-3, respectively shown in FIG. 9, is illustrated schematically in FIG. 17 and structurally in FIG. 18. As shown in those figures, the common permanent magnet 247 may be pill-shaped, being provided with a pair of multiple-arm magnetic structures 331 and 333. The first magnetic structure 331 serves to couple the permanent magnet 247 to the inner pole pieces 235-1, 235-2, and 235-3 of the respective phase I stators 33a-1, 33a-2, and 33a-3. Similarly, the magnetic member 333 serves to couple the permanent magnet 247 to the outer set of pole pieces 237-1, 237-2, and 237-3 of the same three stators.

More-particularly, the first magnetic member 331 is provided with a generally pill-shaped core adapted to efficiently couple magnetically to the bottom .of the pill-shaped magnet 247. A set of three arms 337, 339,

and 341 extend from the head of the magnetic member 331 and upon these arms are wound the three individual compensating coils 251-1-1, 251-1-2, and 251-- l-3, respectively. The three arms 337, 339, and 341 terminate at the pole pieces 235-1, 235-2 and 235-3, as indicated at 343, 345, and 347, to establish a magnetic flux path to respective ones of them from the bottom face of the permanent magnet 247. The opposite, or top, face of the permanent magnet is similarly coupled to the head of the second magnetic coupling member 333, which also is provided with a set of three arms, two of them shown as 349 and 333, and, respectively engaging the stator pole pieces 237-1, 237-2, and 237-3 at the points 353, 355, and 357.

The arrangement illustrated in FIGS. 17 and 18 has two significant advantages. The most apparent of these is that one permanent magnet serves the function previously performed by three, saving weight, size, and cost. A less immediately apparent advantage is that when one of the compensating coils 251-1-1, 251-1-2, and 251-1-3 is energized so as to counteract the flux which would otherwise steadily flow from the permanent magnet 247 across the teeth of the respective stators 33a-1, 330-2, and 330-3, the flux which they produce does not tend to demagnetize the permanent magnet 247. Instead, the flux which is generated by any one of the three coils flows through the magnetic structure associated with the other two of those coils so as to bypass the permanent magnet 247 without tending to demagnetize it. Were this not the case, and were each stator to have its own permanent magnet and its own individual coil as shown, for example, in FIG. 7, the magnetomotive force produced when the coil is energized would tend to demagnetize the permanent magnet, there being no other path through which the flux produced by energization of that coil could pass. Moreover, in returning through the magnetic structures associated with the other two coils, the compensating flux is in a direction such that it tends to reinforce the flux produced through those structures by the permanent magnet 247.

What is claimed is:

1. A display device comprising in combination a. a plurality of indicia-carrying rotors, each having a plurality of magnetic domains;

b. a first, a second, and a third multi-pole stator associated with, and magnetically coupled to the "domains of, each said rotor;

c. common means for periodically altering the magnetization of all of said first stators together in response to a first series of electric pulses;

d. means for steadily magnetizing each of said second stators; and

e. individual means for periodically altering the magnetization of at least one of said second and third stators associated with each said rotor independently of the other stators in response to respective additional series of pulses of a different phase from said first series of pulses.

2. A display device in accordance with claim 1 and characterized further a. in that said individual means includes a separate coil coupled magnetically to each of said second stators only, and

b. in that said third stators are provided with second common means for periodically altering their magnetizations together in response to a third series of electric pulses of a different phase from said first and additional series of pulses.

3. A display device in accordance with claim 1 characterized further in that said individual means includes a separate coil coupled magnetically to each of said third stators only.

4. A display device in accordance with claim 1 characterized further in that said common means includes a single electric coil coupled magnetically to all of said first stators.

5. A-display device in accordance with claim 1 characterized further in that said means for steadily magnetizing includes a single permanent magnet magnetically coupled to all of said second stators.

6. A display device in accordance with claim 5 characterized further in that said second common means includes a single electric coil coupled magnetically to all of said third stators.

7. A display device in accordance with claim 3 and characterized further in that said common means for periodically altering the magnetization of all of said first stators includes a single electric coil coupled magnetically to all of said first stators.

8. A display device comprising in combination a. a plurality of indicia-carrying rotors each having a plurality of magnetic domains;

b. a first, a second, and a third multi-pole stator associated with and magnetically coupled to the domains of each said rotor, poles of a given stator being concurrently aligned with a corresponding plurality of domains on its associated rotor, poles of the respective stators associated with a given rotor being aligned with the domains of said rotor at successive positions of said rotor;

. first common means for periodically magnetizing all of said first stators together in response to a first series of electric pulses;

d. second common means for magnetizing all of said second stators together in response to a second series of electric pulses;

e. means for steadily magnetizing each of said third stators; and

f. individual means for modulating the magnetization of each of said third stators separately in response to respective additional series of electric pulses.

9. A display device in accordance with claim 8 and characterized further in that said first and second common means each include an electric coil and a flux path of magnetic material for magnetically linking it to said second and third stators, respectively.

10. A display device in accordance with claim 9 and characterized further in that said means for steadily magnetizing includes a permanent magnet and said means for modulating comprises an electric coil.

11. A display comprising in combination a. a plurality of indicia-carrying rotors, each having a plurality of magnetic domains;

b. a first, a second, and a third multi-pole stator associated with, and magnetically coupled to the domains of, each said rotor;

c. common means for periodically magnetizing all of said first stators in response to a first series of electric pulses together;

d. means for steadily magnetizing each of said second stators; and

e. individual means for periodically magnetizing each of said third stators independently of the other in response to respective additional series of pulses.

12. A display device in accordance with claim 11 and characterized further in that said common means includes an electric coil and a flux path of magnetic material coupling said coil magnetically to said first stators, said means for steadily magnetizing includes at least one permanent magnet, and said individual means includes, for each of said third stators, an electric coil and a flux path coupling'it magnetically to its associated third stator.

# i i t i 

1. A display device comprising in combination a. a plurality of indicia-carrying rotors, each having a plurality of magnetic domains; b. a first, a second, and a third multi-pole stator associated with, and magnetically coupled to the domains of, each said rotor; c. common means for periodically altering the magnetization of all of said first stators together in response to a first series of electric pulses; d. means for steadily magnetizing each of said second stators; and e. individual means for periodically altering the magnetization of at least one of said second and third stators associated with each said rotor independently of the other stators in response to respective additional series of pulses of a different phase from said first series of pulses.
 2. A display device in accordance with claim 1 and characterized further a. in that said individual means includes a separate coil coupled magnetically to each of said second stators only, and b. in that said third stators are provided with second common means for periodically altering their magnetizations together in response to a third series of electric pulses of a different phase from said first and additional series of pulses.
 3. A display device in accordance with claim 1 characterized further in that said individual means includes a separate coil coupled magnetically to each of said third stators only.
 4. A display device in accordance with claim 1 characterized further in that said common means includes a single electric coil coupled magnetically to all of said first stators.
 5. A display device in accordance with claim 1 characterized further in that said means for steadily magnetizing includes a single permanent magnet magnetically coupled to all of said second stators.
 6. A display device in accordance with claim 5 characterized further in that said second common means includes a single electric coil coupled magnetically to all of said third stators.
 7. A display device in accordance with claim 3 and characterized further in that said common means for periodicallY altering the magnetization of all of said first stators includes a single electric coil coupled magnetically to all of said first stators.
 8. A display device comprising in combination a. a plurality of indicia-carrying rotors each having a plurality of magnetic domains; b. a first, a second, and a third multi-pole stator associated with and magnetically coupled to the domains of each said rotor, poles of a given stator being concurrently aligned with a corresponding plurality of domains on its associated rotor, poles of the respective stators associated with a given rotor being aligned with the domains of said rotor at successive positions of said rotor; c. first common means for periodically magnetizing all of said first stators together in response to a first series of electric pulses; d. second common means for magnetizing all of said second stators together in response to a second series of electric pulses; e. means for steadily magnetizing each of said third stators; and f. individual means for modulating the magnetization of each of said third stators separately in response to respective additional series of electric pulses.
 9. A display device in accordance with claim 8 and characterized further in that said first and second common means each include an electric coil and a flux path of magnetic material for magnetically linking it to said second and third stators, respectively.
 10. A display device in accordance with claim 9 and characterized further in that said means for steadily magnetizing includes a permanent magnet and said means for modulating comprises an electric coil.
 11. A display comprising in combination a. a plurality of indicia-carrying rotors, each having a plurality of magnetic domains; b. a first, a second, and a third multi-pole stator associated with, and magnetically coupled to the domains of, each said rotor; c. common means for periodically magnetizing all of said first stators in response to a first series of electric pulses together; d. means for steadily magnetizing each of said second stators; and e. individual means for periodically magnetizing each of said third stators independently of the other in response to respective additional series of pulses.
 12. A display device in accordance with claim 11 and characterized further in that said common means includes an electric coil and a flux path of magnetic material coupling said coil magnetically to said first stators, said means for steadily magnetizing includes at least one permanent magnet, and said individual means includes, for each of said third stators, an electric coil and a flux path coupling it magnetically to its associated third stator. 